Hi there,
First of all, let it be clear: I work at Thecus! I'll try to be as objective as possible.
Thecus UI was not very friendly. This was one of our major issue. But we've corrected it. Now it's much easier than before: you just type which function you need and you'll arrive wherever you want. It's the most convenient way we found to allow you to browse among dozen of functions/options. And the job gets done: the NAS is stable and well protected. Most important: our UI goes straight to the point.
We'll deploy more functions during 2012 and keep tweaking our UI a bit.
Concerning add-on module, I'm happy to tell you GregN (hi Thecus fan by the way) that you're wrong

We've got a built-in module system and now more than 40 certified apps exist. You can find all of them on the dedicated forum:
http://forum.thecus.com/viewforum.php?f=36 I've tried myself almost of all of them, and it's a huge added value to Thecus NAS.
Concerning Time Machine (for Oymd) I can assure you it's working with all our V5 compatible NAS, I've tried it myself yesterday on a colleague's computer with a N7700. This page of the user manual refers to the fact that Acronis is not working on Mac. It's another topic

You have a tutorial here
http://www.thecus.com/download/howtoguide/HowtoConnectThecusNASwithMacTimeMachine.pdf (just realized we need to update for Lion, it's much easier now)
Depending on your budget, you might want to wait for our N4800 which is a 4 bay NAS with HDMI output. We're now working on embedding XBMC on it. It also features our famous built-in battery and Dual DOM for extra layers of security. It should arrive end of February. You can see me presenting it here:
http://www.youtube.com/watch?v=f_naGAC8hlY
As a regular NAS user, I can tell you this one is going to be huge, i'm super impatient to get one.
I think I've answered everything. I'm not supposed to be on American forums, I spend most of my time on Europeans one, so I'm not sure I'll have time to come here very often

But I'll follow this subject and if anyone got any question about Thecus NAS, feel free to drop me a private message, I'll answer for sure!
EDIT: this review just came out from Legit Reviews
http://www.legitreviews.com/article/1827/11/
I quote
"The last Thecus NAS I reviewed was the N4100Pro back in January of 2009. Since then Thecus has come a LONG way on their NAS interface. The Thecus N5500 layout is nicely laid out and very intuitive. The configuration of the unit from first discovery to formatting the RAID was less than 15 minutes."
Vincent for Thecus